jam640 - 7-11-2007 at 03:46
I was curious on how much diethyl ether gas that had to be present for a flammable/explosive mixture should form.
The lower flammable limits for diethyl ether seem to vary from source to source but in general lies within 2 to 3 percent.
If we have a confined room of 16 cubic meter, how much ether do you have to evaporate in order to "get ignition"?
2% of 16 m3 is 0.32 m3
If we use the ideal gas law, 0.32 m3 of diethyl ether is equal to:
n = PV/RT = (101325*0.32)/(8.314472*293.15) = 13.3 mole
13.3 mole diethyl ether = 13.3*74.12 g/mol = 985.8 g = 1381.8 mL
Am I missing something, or is this correct? 1.4 liter seems pretty much. 
[Edited on 7-11-2007 by jam640]
Per - 7-11-2007 at 12:00
You can´t calculate so.
In the praxis the ether vapours wouldn´t distribute like in your theory.
The most important thing by working with ether is that it could be ignited at just 140°C.
jam640 - 7-11-2007 at 12:33
No, of course the fume concentration would be very much higher closer to the source but in _theory_ and assuming the air/solvent system was
distributed equally. But then, thinking about it 1.4 liter doesn't seem so much. This was not meant to be an real life example. 
jokull - 7-11-2007 at 12:51
Hi
Your arithmetics are right, but there are some important definitions you need to understand clearly:
- Ignition is the point at which combustion starts.
- Combustion occurs when you complete the "fire triangle", i.e. you must have a fuel (diethyl ether), an oxidant (oxygen from air in the room), and a
heat source (a spark or something like that).
- The autoignition point is when you reach the minimum temperature required to ignite a gas or vapor in air without a spark or flame being present,
i.e. you only need a heat surface.
160° C is the temperature corresponding to the autoignition point of diethyl ether.
Coming back to your question, the volume of diethyl ether you calculated actually forms the F/E mixture with the air within your 16m3 room, but it
will never ignite without a heat source.
smuv - 7-11-2007 at 20:06
I have a story about ether pertinent to this subject...
I had a mixture of heptane and ether (say 5% ether rest heptane, an estimate, I thought it was MUCH less concentrated at the time), it was left over
from separating ether from cold starting fluid (for cars and lawnmowers etc.). I put it in an alcohol lamp to see how it would burn as i had about a
gallon of the stuff and was trying to find good use for it. I was about to light the wick with a little microtourch (essentially a glorified
lighter), I pressed a little button and the torch lit, it was maybe 20 inches (50cm for metric folk) away from the 'alcohol' lamp. In the blink of an
eye a pretty fierce flame flashed back to the lamp (luckily a piece of paper on the bench didn't catch fire) and the wick began burning.
Ok maybe not the craziest story? I was in my basement, which is a really large room, there was very little ether around (maybe 10-15 ml total in that
solution if even) but the air above that lab bench was sufficiently saturated with ether to support a flame (I don't think the heptane played much
roll in this as it has a much higher autoignition temp and wider flammability limits). At any rate, I once thought like you, that i'd be passing out
before the flammability limits of ether are reached, but in low lying areas (the surface of my lab bench) the fumes really do concentrate, and ether
really doesn't need to fill a room to be at its explosive limits.
Anyways I hope you liked my story (p.s. heptane does not work well in alcohol lamps, as you may have guessed)
WizardX - 7-11-2007 at 21:28
NIOSH Pocket Guide to Chemical Hazards http://www.cdc.gov/niosh/npg/
Download a stand-alone HTML version of the NPG compressed as a ZIP file. The ZIP file contains a condensed version of the NPG. All non-Pocket Guide
links were removed so that this set of files acts as a "stand-alone" database. These files can be used with a standard web browser or on some mobile
devices
Ethyl ether, C2H5OC2H5
Exposure Limits: TWA 400 ppm (1200 mg/m3), Class IA Flammable Liquid: Flash Point below 73°F and BP below 100°F.
Conversion: 1 ppm = 3.03 mg/m3
Air concentration of 400 ppm (1200 mg/m3) is the max exposure limit and with a Flash Point below 73°F, this is the maximum flammable/safety limits
for diethyl ether.
Bolt - 8-11-2007 at 15:49
Don't forget about the peroxides that supposedly form in old diethyl ether that has no antioxidant present.
I don't know what personal hazard that poses.
smuv - 8-11-2007 at 15:59
It poses and explosion hazard (search the forum)
[Edited on 8-11-2007 by smuv]
chemrox - 8-11-2007 at 21:35
The biggest problem with ether that isn't addressed in any of this, except maybe Smuv's faux pas, is its tendency to form very dense vapors that go
over the sides of any vessel and crawl along surfaces to the floor and where possible beneath. Did you see The Blob? - the original with Steve
McQueen? Ether is like the Blob. If you have a furnace or hot water heater in the basement ether will find it. The vapor concentration in any one
place can't be calculated because of the varying density of it. It may even form turbidity currents along surfaces. If a few precautions are taken
its a nice solvent to work with, low toxicity, pleasant smell, less likelihood of forming emulsions, solvent for organo-metals, good all around
non-polar solvent, flashes off easily (high vapor pressure)... etc. Let me count the ways...Downsides: very hygroscopic, heavy vapor as above,
volatile and flammable, intoxicating vapors. Fire Marshalls aren't so sanguine about it..